Add HostingEnvironment.MapPath

[benamada]

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PR Title
Add HostingEnvironment.MapPath

PR Description
This PR adds a MapPath method to HostingEnvironment. It essentially just calls the existing IMapPathUtility.MapPath() method that HttpServerUtility.MapPath calls. With the new HostingEnvironment.MapPath method, an HttpContext is not required. Before IMapPathUtility.MapPath() is called, there's 2 checks to match the input HostingEnvironment.MapPath accepts in .NET Framework.

• HostingEnvironment.MapPath doesn't accept paths such as file.txt. In contrast, HttpServerUtility.MapPath does accept this. To match HostingEnvironment.MapPath in .NET Framework, the new code throws an exception.
• HostingEnvironment.MapPath does accept paths that are UNC like, e.g. \\file or //file, however MapPathUtility.MapPath() throws an error. To avoid the error and conform with the behavior in .NET Framework (without modifying MapPathUtility.MapPath()), the inbound virtualPath is modified by collapsing multiple leading slashes to a single slash, e.g. /file.

Addresses #460

[benamada]

@dotnet-policy-service agree

[twsouthwick]

Looks good @benamada - can you add some tests?

[twsouthwick]

We're getting ready for a 2.0 release that if you can get that in the next couple days, it'll probably make it in

[benamada]

@twsouthwick I added a new HostingEnvironmentTests.cs file in the Microsoft.AspNetCore.SystemWebAdapters.Tests project.

While testing, I discovered there's a small glitch with the original MapPathUtility.MapPath() method and made a small update to it. In .NET Framework, if the input to Server.MapPath and HostingEnvironment.MapPath includes a trailing slash, e.g. /file/, both MapPath methods return a physical path with a trailing slash. MapPathUtility.MapPath() (this project) always removes trailing slashes. This is a problem if there's code such as MapPath("/path/") + "file.txt" which would incorrectly become /pathfile.txt as opposed to /path/file.txt. The update to MapPathUtility.MapPath ensures the return string includes/excludes a trailing slash based on whether the input has a trailing slash.

Glad to hear this update has a chance to make the 2.0 release. If there's anything else you'd like to see, just let me know.

[twsouthwick]

This looks great! Thanks for the contribution

[benamada]

@twsouthwick good point, I added new tests in HttpServerUtilityTests and HostingEnvironmentTests for ~/ and /.

I initially had these tests in yesterday but they were failing on Linux and macOS. Digging into it further today, the values returned from MapPath() were correct and it was the expected values that were not being put together correctly, e.g. /apps/test-map-path// with a double trailing slash. Updated the tests today to account for this and they are passing now on all platforms.